Q & A > Question Details
I am looking after Atmospheric Distillation unit. Lab results states that RCO flash is always less than HGO (Heavy gas oil/ JBO) flash. As RCO is heavier than HGO what is the reason behind it?
HGO product passes through a stripper; can this be the reason?
08/02/2018 A: Sridhar Balakrishnan, Bharat Oman Refineries Limited , laksrid@yahoo.com
Flash Point of reduced crude oil is lesser than heavier gas oil the reason is that , some of lighter dissolved hydrocarbon gases in the stream , so the flash point is less . If stripper is available , flash point would have been higher . Recommend to do the atmospheric distillation ( ASTM D86) ( up to 300deg. C ) in Laboratory to find for some lighters present in RCO. IBP will indicate the presence of some lighters and indicate the lower flash point.
06/02/2018 A: Eric Vetters, ProCorr Consulting Services, ewvetters@yahoo.com
The flash point for heavier streams is normally dictated by the amount of light ends absorbed into the stream in the fractionator, not by its inherent boiling characteristics. Since a product stripper removes those light ends, it can cause the flash point to increase significantly compared to not having a stripper.
06/02/2018 A: Rajkumar Chate, Sulzer, rajkumar.chate@sulzer.com
Flash point is related to light components and 5% of the product. If you do not have enough trays in stripping section of CDU or if there is not enough stripping steam to stripp the light components then you can expect lower flash point.
This problem started after shutdown or it is a long time on going issue? if it is after shutdown then there is high chance that trays in stripping section might be collapsed and little/no stripping happening. If it is long time persistent problem then solution could be incrase stripping steam (of course you have to check the tray capacity with increased steam) and if possible add few more trays in stripping section of main column during next shutdown.
Trays in stripping section have high liquid load and low vapor load i.e V/L ratio is not properly balanced. Generate the vapor liquid loadings in any simulator with plant data and check the performance of installed trays.
06/02/2018 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
In general, the higher the average boiling point of the sample, the higher is the temperature at which it will flash. Either steam or reboiler stripping will increase the flash temperature.